The present invention relates to a thermal transfer printer, and particularly to a color thermal transfer printer having a simplified structure and an improved printing speed.
A color thermal transfer printer prints an electrical image onto a sheet of paper, which is the so-called video printer. In such color thermal transfer printers, certain color dyes coated on a film ribbon are sublimed into a predetermined pattern by a thermal print head, and the sublimed dyes are transferred onto paper. Then, three color dyes such as yellow, magenta and cyan are overlapped according to color-separated picture units to produce a full color image.
FIG. 1 illustrates a conventional color thermal transfer printer.
The printer is constructed in such a manner that thermal printing of an image is carried out while a sheet of paper 2, the printing medium is rolled around the periphery of a platen drum 1 of a large diameter, wherein a thermal print head 3 pressed against the periphery of platen drum 1 is installed on the upper part of the platen drum 1 of a large diameter to be revolvable by an extra support, a color ribbon taken out of cartridge 4 is positioned between thermal print head 3 and platen drum 1, and a pair of guide rollers 6 for guiding the sheet of paper 2 to the platen drum 1 is provided near the platen drum 1.
The conventional thermal transfer printer as constructed above is disadvantageous in that the planten drum 1 needs to be of a very large diameter since the sheet of paper 2, which is a specific length, must be entirely rolled around the periphery of the platen drum 1 without the sheets ends overlapping each other. Thus, the large diameter of the platen drum increases the overall dimensions of the printer, particularly its height.
To improve this structural disadvantage, a thermal transfer printer as shown in FIG. 2 has been recently developed.
The newly developed thermal transfer printer, contrary to the aforesaid conventional printer, is constructed in such a manner that a sheet of paper is not rolled around a platen drum. That is, the size of the platen drum 1' which the thermal print head contacts, is reduced to a smaller diameter so that the whole sheet can no longer be rolled around the platen drum as before. Instead, the sheet of paper 2' passes through the platen drum 1' while in contact with the drum. A carrier conveys the sheet in a slow, progressive manner forward and backward for a predetermined and sufficient distance. The carrier includes a clamp 7 for clamping and releasing the front edge of the sheet of paper 2' by an operating device, a guide rod 7' for guiding the clamp 7, and an extra driver for forward and backward movement of the clamp 7.
Further, the conventional thermal transfer printer requires a very long paper supply section to provide a sufficient paper-carrying distance, which includes paper guiding plate 9 along curved path P starting from the upper rear of paper tray 8, and a plurality of paper guiding rollers 10 located along path P. This particular conventional structure where papers are supplied via curved path P in the opposite direction of platen drum 1', requires a very complicated power transmission mechanism. In addition, the conventional printer takes an overly long time to carry the paper through a long paper-carrying distance and to print while moving the sheets of paper forward and backward.